Typical examples of the applications of the oscillator as mentioned above include an electromagnetic vibratory part feeder using oscillations generated by an electromagnetic coil, for example. The part feeders of this kind include a part feeder provided with a circular bowl in which a part-transport path in a spiral shape is formed, and which stores parts such as projection nuts (refer to Patent Literature 1, for example).
The circular bowl of the vibratory part feeder of this kind has a part-transport path in a spiral shape formed along an internal wall surface. An attracted portion fixed on a back surface of a bottom portion of the bowl is supported by top ends of a plurality of spring members, and bottom ends of the plurality of spring members are fixed at a predetermined inclined angle to a base member in a stationary state. An electromagnetic coil is provided on the base member, and the attracted portion is intermittently attracted by turning ON/OFF of power supply to the electromagnetic coil, thereby imparting a composed oscillation in a circumferential direction and a vertical direction to the bowl. As a result, a large number of parts fed to the bottom portion of the bowl are sequentially transported in an aligned state along the part-transport path, and are fed out from a feed-out tube on a top end portion of the bowl.
The vibratory part feeder disclosed in Patent Literature 1 provides control of always maintaining a constant amplitude of the part feeder within a drive circuit without providing a special detector for detecting an oscillation state to a main unit of the part feeder in response to a change in weight of the parts in the bowl caused by the feed-out of the parts, or a slight variation in power supply voltage caused by electric power used in a plant.
In other words, the vibratory part feeder is configured to detect, by current detection means, a current flowing through the electromagnetic coil, decompose, by higher harmonic analysis means, the detected current into higher harmonic components, compare and calculate, by oscillation calculation means, a high-order current signal based on an oscillation of a mechanical system out of the higher harmonic components and a set current signal set in advance for generating a predetermined amplitude, and control a drive current of a drive power supply according to the calculated result so that a detected current value and a set current value coincide with each other.
The vibratory part feeder disclosed in Patent Literature 1 uses the current, particularly, a correlation between the current component of the higher harmonic based on the mechanical system of the part feeder and the amplitude. Therefore, the entire processing is carried out by the electronic circuit in a control device without providing a special detector to the main unit of the part feeder, thereby providing an appropriate feedback control of the amplitude following a variation in the part weight or the like.